Knix SuperPlus Leakproof No- Show High Rise Underwear
Skip unless Knix discloses waterproof coating chemicals.
Leakproof coatings commonly rely on PFAS-based water-repellent coating treatments, but Knix doesn't disclose coating chemistry or PFAS status. Third-party testing would help.
The safe swap
Lola
The Lola High Waist Period Underwear
100/100 safety
Same rubric that flunked this product. The swap earned Excellent.
Still want this one anyway? Check the price on Amazon. We’d swap it.
Material
Cotton/synthetic blend with proprietary waterproof/leak-resistant coating (unspecified)
Brand disclosure
Brand is silent on PFAS
Lab data
No public lab test
What’s concerning
Waterproof / stain-resistant treatment
Water-repellent treatments have historically contained PFAS chemicals.
Category baseline
PFAS exposure happens more often with clothing products.
No PFAS disclosure
The company has not publicly discussed PFAS in this product.
Undisclosed waterproof coating chemistry (likely fluorinated or silicone polymer)
The proprietary coating is necessary for leak resistance but Knix has not publicly named the chemical type or stated whether it is PFAS-free. Historical industry practice suggests potential use of fluorinated water-repellents, though silicone alternatives exist. Degradation with washing and heat may increase skin contact over the product lifetime.
Coating degradation and microparticle shedding with repeated wash cycles
Synthetic waterproof coatings on textiles degrade gradually with laundering, especially in hot water or with mechanical stress. Fine particles or coating flakes may shed into wash water or remain on skin; long-term exposure safety is not well characterized for this emerging product category. Replacement every 6-12 months is recommended partly because coating efficacy decays.
What’s reassuring
Formaldehyde / VOCs
No specific findings on record for Knix period underwear. Low-level formaldehyde use in synthetic textiles is common for wrinkle resistance and dye permanence, but cotton-blend construction and non-obvious synthetic finish suggest likely minimal use. Lack of OEKO-TEX certification means no independent verification of formaldehyde limits.
Source: ATSDR ↗Heavy metals
Knix products are typically black or neutral colors, which may use carbon black or low-risk dyes, but no public testing or brand statement confirms exclusion of restricted azo dyes or metal salt dyes. No recalls or contamination reports exist for this product.
Source: FDA ↗Skin sensitization to coating residues or undisclosed polymers
No specific adverse-event reports are on record for Knix period underwear. However, the proprietary coating applied directly to skin-contact areas poses a theoretical risk if chemical residues remain after manufacturing or washing. Individuals with sensitive skin or polymer allergies should consider patch testing or requesting safety data from the brand.
The full breakdown
What it's made of and why it matters
Knix SuperPlus combines cotton and synthetic fibers with a proprietary waterproof/leak-resistant coating that the brand does not publicly identify by chemical name. This coating is the core functional element but also the primary source of concern, as synthetic waterproof finishes on textiles traditionally rely on fluorinated or silicone-based polymers. Cotton itself is low-risk; the blend ratio and coating durability under repeated washing determine safety exposure over product lifetime.
The brand's record and disclosure
Knix has not publicly disclosed the chemical composition of its waterproof coating, which is unusual for a premium period-care brand in a market increasingly attentive to PFAS and chemical transparency. The brand has marketed sustainability and comfort but has not obtained third-party certifications (e.g., OEKO-TEX, GOTS) that would verify absence of restricted chemicals. No major safety recalls or contamination findings are on public record for this product line.
How it compares in its category
Period underwear is a newer category without standardized safety benchmarks. Knix competes with brands like Thinx, Aisle, and Modibodi, many of which also use proprietary coatings but sometimes claim PFAS-free or disclose alternatives (e.g., silicone-based without fluorine). Knix's silence on coating chemistry places it in a less transparent position than some competitors, though no public testing has confirmed higher PFAS levels than rivals.
If you buy it
Wash in cold water and avoid heat drying; tumble dry low or air dry to prevent coating degradation, which can increase leaching and reduces product lifespan. Replace every 6-12 months depending on wash frequency, as waterproof coatings degrade over time and efficacy declines before visible damage occurs. Do not bleach or use fabric softeners, which can compromise the coating. If you have concerns about synthetic coating exposure, contact Knix directly to request coating chemical disclosure before purchase.
What we don’t know
- Basis
- Model estimate, 45% confidence, not a lab result
- Lab test
- None on record for this exact product
- Brand statement
- Knix has made none
Formulations change between production runs, so check the current label. How we grade.
Safer alternatives in Period Underwear
Modibodi
Basic Mid-Rise Period Brief
organic cotton blend with water-resistant coating
Water-resistant coating degradation
Limited concern
Microbial growth and odor with improper care
Limited concern
Lower concern. MADE SAFE certified, PFAS-free claimed and tested.
✓Lab test found no PFAS
Lola
The Lola High Waist Period Underwear
organic cotton with water-resistant treatment
Water-resistant coating degradation and microplastic shedding
Limited concern
Allergen sensitivity to cotton or treatment additives
Limited concern
Lower concern; PFAS-free certified, organic cotton base.
✓Lab test found no PFAS
Lola
Organic Cotton Period Underwear
organic cotton with gusseted absorbent layer
Formaldehyde / VOCs
Limited concern
Azo dyes and color fastness
Limited concern
Microplastic shedding
Limited concern
Lower concern. Organic cotton core, no water-resistant treatment disclosed.
⚠Risky category by default
More period underwear grades
How we score: every product runs through the same public 0–100 rubric based on materials, coatings, brand disclosure, lab findings, and recalls. See the full methodology → Spotted a mistake? Report an error.